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bpf: fix VM out of bounds LoadMemShift check

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The bpf VM did not correctly check the bounds of LoadMemShift
instructions, as it used a size of 0 instead of the correct 1.

A LoadMemShift instruction 1 past the end of the input resulted in a
runtime panic:

    panic(0x5c1d40, 0x7cec00)
            /usr/local/go/src/runtime/panic.go:522 +0x1b5
    golang.org/x/net/bpf.loadMemShift(...)
            /home/afabre/go/pkg/mod/golang.org/x/net@v0.0.0-20190603091049-60506f45cf65/bpf/vm_instructions.go:137
    golang.org/x/net/bpf.(*VM).Run(0xc00000ec40, 0xc0000173c8, 0x2, 0x8, 0x2, 0xc0000173c8, 0x0)
            /home/afabre/go/pkg/mod/golang.org/x/net@v0.0.0-20190603091049-60506f45cf65/bpf/vm.go:131 +0xb0a

Fix this, and rework the out of bounds tests for load instructions to:

* Use an offset one past the end of the input, to catch this

* Use a filter that returns 1, to catch cases were the out of bounds
load does not cause a panic, but does not cause the VM to return 0.

Change-Id: I1e68886915207a34f59765805f907f36dc031f70
Reviewed-on: https://go-review.googlesource.com/c/net/+/180979
Run-TryBot: Matt Layher <mdlayher@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matt Layher <mdlayher@gmail.com>
This commit is contained in:
Arthur Fabre
2019-06-07 15:59:01 +01:00
committed by Matt Layher
parent 1492cefac7
commit 27ecd3f315
2 changed files with 47 additions and 34 deletions
Download Patch File Download Diff File Expand all files Collapse all files

3
bpf/vm_instructions.go
View File

@@ -129,7 +129,8 @@ func loadIndirect(ins LoadIndirect, in []byte, regX uint32) (uint32, bool) {
func loadMemShift(ins LoadMemShift, in []byte) (uint32, bool) {
offset := int(ins.Off)
if !inBounds(len(in), offset, 0) {
// Size of LoadMemShift is always 1 byte
if !inBounds(len(in), offset, 1) {
return 0, false
}

78
bpf/vm_load_test.go
View File

@@ -13,55 +13,61 @@ import (
)
func TestVMLoadAbsoluteOffsetOutOfBounds(t *testing.T) {
pkt := []byte{
0xff, 0xff, 0xff, 0xff,
0xff, 0xff, 0xff, 0xff,
0, 1, 2, 3,
}
vm, done, err := testVM(t, []bpf.Instruction{
bpf.LoadAbsolute{
Off: 100,
Size: 2,
Off: uint32(len(pkt)),
Size: 1,
},
bpf.RetA{},
// Out of bounds should return 0, return 1 to tell if execution continued
bpf.RetConstant{Val: 1},
})
if err != nil {
t.Fatalf("failed to load BPF program: %v", err)
}
defer done()
out, err := vm.Run([]byte{
0xff, 0xff, 0xff, 0xff,
0xff, 0xff, 0xff, 0xff,
0, 1, 2, 3,
})
out, err := vm.Run(pkt)
if err != nil {
t.Fatalf("unexpected error while running program: %v", err)
}
if want, got := 0, out; want != got {
t.Fatalf("unexpected number of output bytes:\n- want: %d\n- got: %d",
t.Fatalf("unexpected result:\n- want: %d\n- got: %d",
want, got)
}
}
func TestVMLoadAbsoluteOffsetPlusSizeOutOfBounds(t *testing.T) {
pkt := []byte{
0xff, 0xff, 0xff, 0xff,
0xff, 0xff, 0xff, 0xff,
0,
}
vm, done, err := testVM(t, []bpf.Instruction{
bpf.LoadAbsolute{
Off: 8,
Off: uint32(len(pkt) - 1),
Size: 2,
},
bpf.RetA{},
// Out of bounds should return 0, return 1 to tell if execution continued
bpf.RetConstant{Val: 1},
})
if err != nil {
t.Fatalf("failed to load BPF program: %v", err)
}
defer done()
out, err := vm.Run([]byte{
0xff, 0xff, 0xff, 0xff,
0xff, 0xff, 0xff, 0xff,
0,
})
out, err := vm.Run(pkt)
if err != nil {
t.Fatalf("unexpected error while running program: %v", err)
}
if want, got := 0, out; want != got {
t.Fatalf("unexpected number of output bytes:\n- want: %d\n- got: %d",
t.Fatalf("unexpected result:\n- want: %d\n- got: %d",
want, got)
}
}
@@ -107,54 +113,60 @@ func TestVMLoadConstantOK(t *testing.T) {
}
func TestVMLoadIndirectOutOfBounds(t *testing.T) {
pkt := []byte{
0xff, 0xff, 0xff, 0xff,
0xff, 0xff, 0xff, 0xff,
0,
}
vm, done, err := testVM(t, []bpf.Instruction{
bpf.LoadIndirect{
Off: 100,
Off: uint32(len(pkt)),
Size: 1,
},
bpf.RetA{},
// Out of bounds should return 0, return 1 to tell if execution continued
bpf.RetConstant{Val: 1},
})
if err != nil {
t.Fatalf("failed to load BPF program: %v", err)
}
defer done()
out, err := vm.Run([]byte{
0xff, 0xff, 0xff, 0xff,
0xff, 0xff, 0xff, 0xff,
0,
})
out, err := vm.Run(pkt)
if err != nil {
t.Fatalf("unexpected error while running program: %v", err)
}
if want, got := 0, out; want != got {
t.Fatalf("unexpected number of output bytes:\n- want: %d\n- got: %d",
t.Fatalf("unexpected result:\n- want: %d\n- got: %d",
want, got)
}
}
func TestVMLoadMemShiftOutOfBounds(t *testing.T) {
pkt := []byte{
0xff, 0xff, 0xff, 0xff,
0xff, 0xff, 0xff, 0xff,
0,
}
vm, done, err := testVM(t, []bpf.Instruction{
bpf.LoadMemShift{
Off: 100,
Off: uint32(len(pkt)),
},
bpf.RetA{},
// Out of bounds should return 0, return 1 to tell if execution continued
bpf.RetConstant{Val: 1},
})
if err != nil {
t.Fatalf("failed to load BPF program: %v", err)
}
defer done()
out, err := vm.Run([]byte{
0xff, 0xff, 0xff, 0xff,
0xff, 0xff, 0xff, 0xff,
0,
})
out, err := vm.Run(pkt)
if err != nil {
t.Fatalf("unexpected error while running program: %v", err)
}
if want, got := 0, out; want != got {
t.Fatalf("unexpected number of output bytes:\n- want: %d\n- got: %d",
t.Fatalf("unexpected result:\n- want: %d\n- got: %d",
want, got)
}
}